Process of producing smoke for treating comestibles and apparatus for practicing such process



June 26, 1951 c. s. M MULLEN 2,558,307

PROCESS OF PRODUCING SMOKE FOR TREATING COMESTIBLES AND APPARATUS FOR PRACTISING SUCH PROCESS 2 Sheets-Sheet l flqi.

Filed June 7, 1947 53 5? 52 38 5o 51 37 36 Q2 93 7Q 49 a1 28 16 5'"? 7 i9 96 Q7 INVENTOR. Claudl S.McMuZZen A TTORNE 1 June 26, 195] c. s. M MULLEN 2,558,307 PROCESS OF PRODUCING SMOKE FOR TREATING COMESTIBLES AND APPARATUS FOR PRACTISING SUCH PROCESS Filed June '7, 1947 2 Sheets-Sheet 2 \JNVENTOR. CZaud SMCMLLZZQn ATTORNEY.

Patented June 26, 1951 PROCESS OF PRODUCING SMOKE FOR TREATING COMESTIBLES AND AP- PARATUS FOR PRACTICING SUCH PROCESS Claud S. McMullen, New York, N. Y., assignor to National Smokehouse Equipment, Inc., Clifton, N. J., a corporation of New Jersey Application June 7, 1947, Serial No. 753,396

11 Claims. 1

This invention relates to a smoke generator for use in producing smoke for the smoke curing or preserving of comestibles, such as meat and fish, and to a novel method of generating such smoke. 3 Smoke generators now available produce smoke of varying density with consequent variationin the color and. other properties, of the egmestibles cured or preserved by treatment therewith. Moreover, such smoke generators are relatively inflexible, i. e., they can be operated at full capacity or not at all. In those cases in which a smoke generator is employed to, supply smoke for a plurality of smoke houses and for some reason it is desired to supply smoketo only some of the houses, the inflexibility of the smoke generator presents a serious problem., Usually the smoke generator is run at its full capacity and the smoke supplied to the smaller number of smoke houses; under these conditions comestibles are subjected to a correspondingly greater volnine of smoke with consequent deleterious effect ongthe product and uneconomic utilization of the sawdust employed to produce the smoke.

Among the objects of this inventionis to provide. a smoke generator which produces a smoke stream of substantially constant density and which is relatively flexible so that it can produce {a desired amount of smoke of substantially conrstant density per unit of time for use in one or more smoke houses and this with economic consumption of the sawdust employed to generate the smoke.

Another object of this invention is to provide a novel method of generating smoke suitable for use in curing or preserving comestibles,

which method resultsin the production of a maximum amount of smoke of substantially constant density and relatively free of tarry constituents per unit amount of sawdust consumed.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

In accordance with this invention a stream of air, preferably under pressure, is introduced into a bed of sawdust and caused to flow first in a generally vertical direction throughout substantially the full depth of this bed, the air supporting combustion of the sawdust and causing smoldering thereof to take place to produce smoke. The smoke thus produced is passed through a horizontal path extending below the surface of the bed of sawdust, whereby tarry constituents are removed from the smoke. The thus filtered smoke is removed from the bed. Desirably the 'air is introduced into the upper portion of the smoke generator at a plurality of spaced points along the width of this generator under superatmospheric pressure of the order of 2to 14 ounces per square inch gauge, is passed downwardly through the full depth of the bed of sawdust and upon reaching the base of the generator passed in a generally horizontal direction through the main bed of sawdust. Operation in this manner effects eificient distribution of air throughout the sawdust in amount to cause smoldering of the. sawdust to take place to produce smoke, and insures the substantially complete utilization of the sawdust to produce smoke. Further the flow of the smoke thus produced through the main bed of sawdust prior to its discharge from the smoke generator causes the smoke to be filtered by this bed of sawdust before leaving the generator thus removing from the smoke tarry constituents and particles of. ash and dust.

In accordance with a preferred embodiment of the invention, the smoke generator comprises a horizontally elongated housing having baffles, disposed near the ends defining vertically extending air inlet and smoke exit chambers positioned at the opposite ends of the housing and a horizontally elongated intermediate chamber. A bed of sawdust which may be hickory or other Wood dust or chips is disposed in the air inlet and in-: termediate chambers; the smoke exit chamber is substantially free of sawdust. Air is supplied to the smoke generator from a main air stream of substantially constant volume per unit of time, which volume, however, can be adjusted in accordance with the amount of smoke desired; thus, if the generator is employed to supply two smoke houses of equal capacity, the volume of. air per unit of time constituting this main air stream would be twice the volume employed to generate smoke for a single such smoke house. This main air stream is divided into two streams, one of which by-passes the body of sawdust, and the other is introduced into the air inlet chamber to support combustion of sawdust therein, the air being admitted in amount to cause smoldering of the sawdust in this chamber and the intermediate chamber to take place to produce smoke. The smoke thus generated is passed through the bed of sawdust in the intermediate chamber below the surface thereof thereby effecting the removal of tarry constituents, ash and dust, from the sawdust. The thus filtered smoke then enters the smoke exit or discharge chamber. From this discharge chamber the smoke enters a smoke main into which also flows the by-passed air pro-,

ducing the desired smoke stream which is fed to one or more smoke houses.

The division of the main air stream into the aforesaid two streams is regulated to produce a desired smoke stream of substantially constant density. The regulation-preferably is carried out by a control involving a pair of temperature re sponsive elements, one positioned in the air stream leading into the air inlet chamber and the other in the smoke exit line, leading into the smoke main where the smoke and by-passed airmix. These temperature responsive elements measure the temperature differential between the temperature of the entering air and the exiting smoke and communicate with a controller which effects operation of valves controlling the inixedwith the smoke generated) to maintain thedensity of the product smoke stream substantially constant.

. I have found that as a general rule variations in the density of the smoke are proportional to variations in the temperature differential between the temperature of the smoke leaving the generator and the temperature of the air entering. By supplying 'a substantially constant volume of air for the production of a desired given amount of smoke and dividing this air stream into two streams, one of which by-passes the bed of sawdust and the other of which is introduced into the bed'of sawdust to support combustion thereof to produce smoke and regulating the division of this main air stream in accordance with variations in the temperature differential between the. temperature of the entering air and the exiting smoke'so as to restore this differential to a predetermined value, a smokestream of constant density is produced. This smoke stream may be employed to cure or preserve comestibles producingsmoked products, the color and other proper.- ties ofqwhich'are markedly more uniform than smoked products heretofore produced.

The optimum differential value for which the control may be set is dependent upon the nature ofthe sawdust and the capacity and design of the smoke generator. For any particular generator and'type of sawdust consumed therein this value may readily be determined by an initial trial run.

" In the, accompanying drawings forming a part of this specification and showing for purposes of exemplification preferred forms of this invention without limiting the claimed invention to such illustrative instances:

Figure 1 is a plan view of a smoke generator embodying a preferred form of this invention;

Figure. 2 is a vertical section taken in a plane passing through line 2--2 of Figure 1;

Figure 3' is an end elevational view of the smoke, generator of Figures 1 and 2;

Figure-4 is a rear elevational view of the smoke generator and shows a photo-electric cell type of-control for 'actuating'the valves in the air inlet and by-pass lines instead of the tempera- 4 ture differential control shown in Figures 1 to 3; and

Figure 5 is a detail view showing a section through the smoke main and a perspective view of the photo-electric cell for receiving light rays from a beam of light passing through the smoke main.

. In the drawings Ill indicates a smoke generator housing which may be in the form of. a rectangular box having metal walls, desirably cast iron or steel. Fire brick or other refractory support II is provided in the base of this housing for supporting a bed of sawdust. Instead of a solid fire brick support, a grate may be employed disposed above the base of the housing, through which grate ash may fall into the base of the housing for ready removal. However, the solid fire brick support which can be cleaned from time to time to remove ash and tarry deposits thereon is preferred. The side and end walls of this housing, are lined with suitable heat insulating material, such as the asbestos cement composition known as Transiteythis lining is indicated by the reference character l2.

Suitably secured to the top of' the housing near the opposite ends thereof are bafiie members l3, [4 extending downwardly from the-top to a point above the fire brick support ll." Baflie l3 extends across the width of the housing and cooperates with end wall [5 to define an 'air inlet chamber l6 extending in a generally vertical direction, i. e., chamber [6 has a somewhat greater vertical extent than the distance between bafile i3 and end wall I5. Baiile I4 is spaced from the opposite end wall ll to define a smoke exit duct or chamber is extending in a generally vertical direction contiguous to the end wall H. B'ailies l3 and I4 define the end walls of an intermediate sawdust receiving chamber l9 which. it 'will' be noted from Figure 2 of the drawings, extends in a generally horizontal direction. Positioned substantially midway between bafiles l3 and I4 is a bailie ZGeXtending from the base of the housing to a point 2| positioned above the terminals of baffles l3 and M. The baffles l3, l4, and 20 desirably are of asbestos cement material, such as Transite, or other fire resistant material.

Iop 22 of the. housing is provided with an ac.- cess opening 23 closed by a suitable cover- 24 through which sawdust may be charged into the housing 10 to produce a bed 25 resting on the refractory support H and disposed within the air inlet chamber l6, and intermediate chamberlS leaving a free space 26 above this bed. .An ac-. cess opening 2'! closed by a suitable cover 28 may be formed in the end walls I! to give access to the smoke discharge chamber other purposes when desired. Y Access openings 29, 30 provided with suitable closures are desira-.

top portion of the air inlet chamber I6 and the.

intermediate chamber 19; sawdust'may be fed through access opening 3| into air inlet chamber I6 to produce a bed of sawdust in this chamber, as shown in Figure 2.

A blower 32 actuated by. a multiple speed motor 33 supplies air to the generator. Blower 32 and motor 33 may be of any known type. which, depending upon the selected speed of operation of the motor, supplies a predetermined- !8 'for cleaning or constant volume of air to the main air line 34 communicating with the blower. If the generator is designed for supplying smoke to four smoke houses; desirably a 4-speed motor is employed, the motor being operated at its maximum speed when all four houses are in operation and being operated at 1st, 2nd or 3rd speeds when l, 2 or 3 smoke houses, respectively, are supplied with smokefrom the generator. A manual control valve in the main air line 34 is provided for controlling the Volume of air delivered by the blower 32 to the main air line 34. This valve may be used with a single speed motor driven fan to control the volume of air delivered by the fan to the main air line; thus, if two smoke houses are supplied with smoke, the valve is set to give a flow per unit of time twice the volume of that employed when only one smoke house is supplied with smoke.

Main air line .34 communicates with two branches. One branch 36 constitutes the air inlet line supplying air to the air inlet chamber It. This branch 36 has a plurality of spaced offtake pipes 31 each provided with a valve 38 and leadinginto the air inlet chamber 16 at spaced points, as indicated in Figure l. branch 39 constitutes an air by-pass line which leads into a smoke main 40 communicating with the. smoke distributing pipes or ducts in the smoke houses.

, .A butterfly valve 4| is positioned in the branch 36 and is arranged to be actuated by a motor 42 of any ,well known type through suitable linkage mechanism 43. A butterfly valve 44 is disposed in the by-pass branch 39 and is arranged to be actuated by a motor 45 of any well known type, desirably the same as that of 42, through the linkagemechanism 46. Valves 4! and 44 are normally positioned to divide the main air stream flowing through line 34 into the branches 35, 39 into two streams bearing a definite volume ratio to each other, one of the streams flowing through line 35, offtake pipes 37 into the air inlet chamber l5 and the other Icy-passing the smoke generator and flowing into the smoke main 49.

g Smoke discharge chamber I8 is provided with a series of spaced offtakes 41, as shown in Figurel, each provided with a valve 48 and leading into a smoke manifold 49 which communicates with the smoke main 40.

Disposed in air inlet branch 35 is a temperature control element 50 responsive to the temperature of the air entering the inlet chamber 16. A like element 5| is disposed in the smoke manifold 49 responsive to the smoke leaving the smoke generator. Elements 59, 5| are connected through conductors 52 with a differential thermostat or other control device 53, which, through conductors54, effects operation of the motors 42, 45 actuating the valves 4|, 44, respectively. The control involving the temperature responsive elements 50, 5|, the differential thermostat 53, and the conductors 52 and 54 may be any well known type of controllersuch, for example, as the remote bulb differential temperature controller commercially available, the differential thermostat of which, for example, may effect opening or closing of electrical switches in circuit with the electric motors 42, 45, therebyenergizing or die-energizing these motors to change the position of the butterfly valves 4| and 44 to cause more or less of the main air stream to flow through branch 36 and less or more of this main air stream, respectively, to flow through by-pass branch 39.

The other The density of the smoke generated will depend chiefly on the amount of air supplied to support combustion of the sawdust, the particle size of the sawdust, the moisture content of the sawdust, the character of the sawdust, i. e., whether hickory or other wood, the time of contact between the air and the sawdust particles, etc. These factors vary during the operation of the generator; thus successive charges of sawdust may have varying moisture contents. As the sawdust is consumed channeling of the air in its flow through the bed of sawdust may take place, the extent of channeling varying with consequent variation in the time of contact between air and sawdust, etc. Hence, as a practical matter it has not been possible with prior designs of smoke generators to produce smoke of substantially constant density.

With my invention, on the other hand, the speed of motor '33 driving blower 32 or valve 35, or both, is set to give a desired volume of air per unit of time, depending upon the amount of smoke desired per unit of time. Controller 53 is then set for a predetermined value, determined by a previous trial run for each particular generator and type of sawdust consumed therein to give a smoke of desired density. The temperature of the smoke entering manifold 49 is dependent chiefly upon the rate of combustionof the sawdust, the amount of sawdust consumed, and the temperature of the air introduced through branch 36. In effect, the division of the constant volume main air stream into two streams, one of which enters the smoke generator and the other by-passes this generator and is mixed with the generated smoke, is varied to maintain a substantially constant differential temperature between the temperature of the inlet air passing through branch 36 and the temperature of the exit smoke passing through branch 49 and thereby produce a desired volume of smoke per unit of time of substantially constant density. Thus, for example, if due to increase in the moisture content of the sawdust, less sawdust is consumed,

1 producing a smoke of decreased density having a lower temperature, the control operates to increase the flow of air into chamber l6 and decrease the flow through by-pass branch 39 causing the generation of more smoke per unit of time with consequent increase in temperature. Similarly, if the temperature of the smoke flowing through line 49 increases for any reason, the control operates to cause less of the main air stream to flow through line 33 and more to flow through by-pass 39 with consequent lower con sumption of sawdust per unit of timeand the production of less smoke at a lower temperature. In effect, during operation the control functions to substantially continuously change the position of the butterfly valve 4|, 44 so that whenever the differential temperature rises above the predetermined value it is brought down to this value and when it falls below this value it is brought up thereto, a constant volume of air flowing through main air line 34, more or less of the air being used to support combustion and less or more by-passed and mixed with the smoke generated to produce a desired volume of smoke product (diluted with air) per unit of time of substantially constant density.

Disposed at the base of the generator housing, just above the fire brick support H where the smoke discharge chamber [8 communicates with the intermediate chamber, is a thermostatic element 55, such as a pyrostat 55, which may be of'any Well'known type. Pyrostat. 55; isllocated at the point. where the last portion. of the bed of sawdust will be. burning. when the bed is substantially completely consumed. Itis in cir- .cuit. through conductors. fifi with motor 33. and through conductors 51 with a bell 58.. Thus, should substantially all of the sawdust.v consti? tilting. the bed be consumed pyrostat 55.0peratcs to shut off motor 33. operating fan 32v to discontinue supply of air to the smoke generator and to ring the alarm 58, thereby calling theop? erators attention to the need for replenishing the :bed of sawdust.

Sawdust may be fed to the generator from an automatic charging device supplying the sawdust through top opening 23, or top sideopening 3|, or both, so as to maintain a bed of sawdust at a desired level within narrow limits. If desired, the generator may be charged man uallyi from time to time as required. The term sawdust is usedherein in. a broad sense and is intended to include wood chips and chips'or dust of other cellulose material suitable foruse in generating smoke for treating cornestibles.

Instead of the differential temperature controller shown in Figure 1, 2 or 3, the photoelectric cell type of control, as shown in Figures 4 and5, may be used. In Figure 5, 59 indicates a. light source from which a beam of light 69 passes across main at and impinges on a photo electric cell SI of any well known type. This cell is in circuit with motors t2 and 45 which efiectoperation of valves 4i and 44. As the density of the smoke stream passing through main 60 varies, the density of the light beam EB-impinging on cell 6| varies correspondingly, causing this cell through suitable amplifiers and relays, as well known in the electrical control art, to effect operation of motors 62 and 65 to divide the main air stream into two streams of varying volume per unit of time. This divisionis such that more air is passed through the generator to generate more smoke when the density falls to restore the density to the desired value and less air is fed to the generator when the denofthis invention produces a smoke stream oi substantially constant density. Further, it is flexible in operation since by suitable selection of motor speed driving the air supply fan or of the valve associated with this fan anydesired volume of smoke may be generated of desirei density to treat comestibles in any reasonable number of smoke houses for any desired treatment time.- Thus with this invention ioursrnoke houses may be supplied with a desired density smoke for say an eight hour process period and if it is necessary at some other time to supply only two of these houses with smoke, by halving the fan speed two such smoke houses can be supplied with the same density smoke for the same process period and this with the, same economical consumption of sawdust,

With the baffie arrangement shown the air is caused to flow vertically through substantially the full depth of the bed of sawdust, and the smoke generated horizontally below the surface of the horizontally elongated bed so that the smoke is filtered, resulting in the production or" relatively clean smoke, i. e., smoke containing little or no ash, dust and tarry constituents. This smoke, if desired, may be subjected to a'water scrubbing treatment by passage through a chem.- ber in which it is scrubbed with water topro-e duce a still cleaner smoke; for example, the smoke stream from main. 49, before entering the smoke distributing pipes or ducts, may be passed through av water scrubber. The. intro. duction of air under pressure, its distribution. as hereinabove described, and the flow of the gen:- erated smoke through the bed of sawdust re.- sults in the most effectiveutilization of thesawdust to generate smoke.

The introduction of the air under pressure in a downward direction in a bed of sawdust supported on a solid fire brick support, as in the preferred embodiment of this invention, avoids agitating the bed so as to cause suspension of the sawdust particles in the air stream with more effective utilization of the sawdust to generate smoke. The flow of this smoke containing un combined or unreacted oxygen through thefbed in a horizontal direction effects cleaning of the smoke as hereinabove described and also most effective utilization of the sawdust to generate smoke.

For initial lighting of the sawdust,. a small gas burner may be, installed at the surface of the bed of sawdust in the air inlet chamber; When this chamber is filled with sawdust, as indicated in the drawing, this burner'is' lit and the air thereafter caused to enter this chamber. Thereafter, the supply of ga to this burner is interrupted, the smoldering sawdustcheating the incoming air'and causing this air to support combustion of additional sawdust to generate smoke.

Since certain changes in carrying out the above 7 process and in the smoke generator, which embody the invention, may be made without departing from its scope, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is: g

1. The method of producing a smoke stream of substantially constant density for treating comestibles, which comprises flowing a stream of air of'substantially constant volume per unit of time, dividing said stream intotwo streams, flowing and regulating the-quantity of one of the two streams in contact with a body of sawdust to support incomplete. combustionof said sawdustand produce. smoke, by-passing the other of said two streams about the said body of'sawdust, mixing the. said smokewith the. by-passed air stream to produce a smoke stream, and regulating said division of said main air stream to maintain thedensity of said" smoke stream substantially constant and produce. a. smoke stream of predetermined constant. density.

2. The method of producing a smoke stream of substantially constant density for treating comestibles, which comprises flowing a main stream of air of substantially constant volume per unit of time, dividing said stream into" two streams, introducing and regulating the quantity 7 of one of the two streams in contact with a body main,

between the temperature of air introduced into contact with the said body of sawdust and the streams, flowing and regulating the quantity of one of said two streams into a horizontally elongated bed of sawdust, directing said air to travel in a generally vertical direction throughout substantially the full depth of said bed to support incomplete combustion of said sawdust and cause smoldering thereof to take place to produce smoke, passing said smoke through a horizontal path extending below the surface of said bed, whereby tarry constituents in said smoke are removed therefrom, withdrawing the thus filtered smoke from the bed, by-passing the other of said air streams about the said bed of sawdust, mixing the by-passed air stream with the said filtered smoke stream to produce a smoke stream, and regulating said division of said main air stream to maintain the density of said smoke stream substantially constant, and produce a smoke stream of predetermined constant density.

4. The method of producing a smoke stream of substantially constant density for treating comestibles, which comprises flowing a main stream of air of substantially constant volume per unit of time, dividing said stream into two streams, introducing one of said streams into the top of a horizontally elongated bed of sawdust, directing said air to travel in a generally downward direction throughout substantially the full depth of said bed at one end thereof and regulating the quantity thereof to support incomplete combustion of said sawdust and cause smoldering thereof to take place to produce smoke, passing said smoke through a horizontal path extending below the surface of said bed of sawdust from the said one end to the other end thereof, whereby the ence between the temperature of the said stream of air introduced into said bed and the temperature of said filtered smoke withdrawn from said bed to produce a smoke stream consisting of the smoke generated mixed with the by-passed air stream of substantially constant density.

5. The method of producing a smoke stream for treating comestibles, which comprises fiow ing a stream of air into a horizontally elongated bed of sawdust, directing said air to travel in a generally vertical direction throughout substantially the full depth of said bed at one end thereof and regulating the quantity thereof to support incomplete combustion of said sawdust and cause smoldering thereof to take place to produce smoke, passing said smoke through a horizontal path extending below the surface of said bed from the first mentioned end of the bed to the other end, whereby tarry constituents in said smoke are removed therefrom, and withdrawing the thus filtered smoke from the other end of said bed.

6. The method of producing a smoke stream for treating comestibles, which comprises introducing, a stream of air under pressure into the top of a horizontally elongated bed of sawdust at one end thereof, directing said air to travel in a generally downward direction at said end throughout substantially the full depth of said bed and regulating the quantity thereof to support incomplete combustion of said sawdust and cause smoldering thereof to take place to produce smoke, passing said smoke through a horizontal path extending below the surface of said. 'bed of sawdust from the said end thereof to the opposite end, whereby the tarry constituentsin said smoke are removed therefrom, and withdrawing the thus filtered smoke from the said opposite end of said bed. j

7. A smoke generator comprising a housing, a support in said housing for a bed of sawdust, bafiies in said housing disposed'near the ends thereof defining an inlet chamber near one end of the housing, a smoke discharge chamber near the opposite end of the housing and an intermediate chamber, said bed of sawdust being dis,-

posed in said inlet and intermediate chambers, means for introducing air into the air inlet chamher and for regulating the quantity thereof to support incomplete combustion of saidsawdust and causing smoldering thereof to take place to produce smoke and for passing said smoke through the bed of sawdust in the intermediate chamber, and means for withdrawing the smoke from the smoke discharge chamber.

8. A smoke generator comprising a horizontal elongated housing, a support in the base of said housing for a bed of sawdust, baffles extending from the top of said housing into said bed of sawdust near the opposite ends of said housing and terminating short of the said support defining a vertically elongated air inlet chamber, a vertical elongated smoke discharge chamber, and a horizontally elongated intermediate chamber, a baflle extending from the base of said housing intermediate the first mentioned baffies to a point above the point of termination of said first mentioned baffles, and means for introducing air under pressure into the air inlet chamber and for regulating the quantity thereof to support incomplete combustion of said sawdust and cause smoldering thereof to take place to produce smoke and for passing said smoke through the bed of sawdust in said intermediate chamber into said smoke discharge chamber, and means for withdrawing the smoke from the smoke discharge chamber.

9. A smoke generator comprising a horizontal elongated housing, a support in the base of said housing for a bed of sawdust, baffles extending from the top of said housing into said bed of sawdust near the opposite ends of said housing and terminating short of the said support defining a vertically elongated air inlet chamber, a vertically elongated smoke discharge chamber, and a horizontally elongated intermediate chamber, a baffle extending from the base of said housing intermediate the first mentioned baiiles to a point above the point of termination of said first mentioned bafiles, means for introducing air under pressure into the air inlet chamber and for regulating the quantity thereof to support incomplete combustion of said sawdust and cause smoldering thereof to take place to produce smoke and for passing said smoke through the 1 bed of sawdust in said intermediate chamber into said smoke discharge chamber, means for withdrawing the smoke from the smoke discharge chamber, means for flowing a stream of air bypassing said housing, means for mixing'said by passed air with the said smoke withdrawn from the'smoke discharge chamber and control means for maintaining the mixture at a substantially constant density.

10. A smoke generator comprising a'housing, a support in said housing for a bed of sawdust,

baflies 'in said housing disposed near the ends thereof defining an air inlet chamber near one end of the housing,.a smoke discharge chamber near the opposite end of the housing and an main air line, two branches leading from said main air line, one leading into the air inlet chamber and the other by-passing the said housing,

a valve in each of said branches, a smoke disintermediate sawdust containing chamber, a'

12 near the-opposite end of the housing and an intermediate sawdust containing chamber, a main air .line, two branchesleading from said main air line, one leading into the air inlet chamber and the other by-passing the saidheusing, a Valve in each of said branches, alsmoke discharge linejleading from said smoke discharge c'onta'iner into said air by-pass branch, a temperature responsive elementin the branch leading into the air inlet chamber, a temperature responsive element in the smoke discharge line, and a control actuated by said temperature responsive elements 'for opening one of said valves while simultaneously closing the other valve in the said branches.

C. S. MCMULLEN.

7 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

